This invention relates generally to method and apparatus for reading a bar code with automatic scanning so that bar-coded information printed on a label or the like which is attached to goods, can be recognized.
Conventionally, a light pen is known as a tool for scanning an image of a bar code by manual operation of movement in a direction normal to the longitudinal direction of each parallel bar of a bar code. However, since a sensor used in a light pen or the like is not of self-scanning type, the reading accuracy is greately affected by the speed of scanning manually performed.
On the other hand, in a bar code reading apparatus of electronic scanning type using an image sensor of self-scanning type, since scanning in a direction normal to the longitudinal direction of the parallel bars is electronically effected, no manual operation is needed. Although scanning can be effected desirably with such an electronic scanning type bar code reading apparatus, such a reading apparatus has suffered from a drawback caused by the use of a lens. Namely, since the image sensor of such apparatus is stationary with respect to the bar code, the image of a bar code on a curved label is apt to be unfocussed in connection with bars at both ends of the label if these bars are located beyond the focal depth of the lens used for condensing the light from the bar code. This tendency increases as the curvature of the bar code label increases. Because of such an unfocussed image on the image sensor, the widths of bars at both ends are apt to be erroneously detected. Furthermore, the bars at both ends will be imaged with narrower images than their actual widths. As a result, a bar code attached to a curved portion is difficult to read, and thus error reading likely occurs. Furthermore, it is impossible to perform reading when the width of a bar code is wider than a single field of vision with which an image can be obtained on the image sensor.
Although a light pen is known as a tool which is capable of scanning in a direction normal to the longitudinal direction of a bar code, it is difficult to scan all the bars at a constant speed along a curved surface by only a manual operation, and thus decoding is difficult, while there is a drawback that error in reading frequently occurs.